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[PATCH v2 2/7] block: add bdrv_replace_node_common()

From: Vladimir Sementsov-Ogievskiy
Subject: [PATCH v2 2/7] block: add bdrv_replace_node_common()
Date: Fri, 6 Nov 2020 15:42:36 +0300

Add new parameter to bdrv_replace_node(): auto_skip. With
auto_skip=false we'll have stricter behavior: update _all_ from
parents or fail. New behaviour will be used in the following commit in
block.c, so keep original function name as public interface.

Note: new error message is a bit funny in contrast with further
"Cannot" in case of frozen child, but we'd better keep some difference
to make it possible to distinguish one from another on failure. Still,
actually we'd better refactor should_update_child() call to distinguish
also different kinds of "should not". Let's do it later.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
 block.c | 25 ++++++++++++++++++++++---
 1 file changed, 22 insertions(+), 3 deletions(-)

diff --git a/block.c b/block.c
index 19db7b7aeb..11c862d691 100644
--- a/block.c
+++ b/block.c
@@ -4563,8 +4563,16 @@ static bool should_update_child(BdrvChild *c, 
BlockDriverState *to)
     return ret;
-void bdrv_replace_node(BlockDriverState *from, BlockDriverState *to,
-                       Error **errp)
+ * With auto_skip=true bdrv_replace_node_common skips updating from parents
+ * if it creates a parent-child relation loop or if parent is block-job.
+ *
+ * With auto_skip=false the error is returned if from has a parent which should
+ * not be updated.
+ */
+static void bdrv_replace_node_common(BlockDriverState *from,
+                                     BlockDriverState *to,
+                                     bool auto_skip, Error **errp)
     BdrvChild *c, *next;
     GSList *list = NULL, *p;
@@ -4583,7 +4591,12 @@ void bdrv_replace_node(BlockDriverState *from, 
BlockDriverState *to,
     QLIST_FOREACH_SAFE(c, &from->parents, next_parent, next) {
         assert(c->bs == from);
         if (!should_update_child(c, to)) {
-            continue;
+            if (auto_skip) {
+                continue;
+            }
+            error_setg(errp, "Should not change '%s' link to '%s'",
+                       c->name, from->node_name);
+            goto out;
         if (c->frozen) {
             error_setg(errp, "Cannot change '%s' link to '%s'",
@@ -4623,6 +4636,12 @@ out:
+void bdrv_replace_node(BlockDriverState *from, BlockDriverState *to,
+                       Error **errp)
+    return bdrv_replace_node_common(from, to, true, errp);
  * Add new bs contents at the top of an image chain while the chain is
  * live, while keeping required fields on the top layer.

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